An amoeboflagellate, Naegleria fowleri, has been identified as the causal agent of a primary meningoencephalitis in man. Cultivation of the amoeba in tissue culture systems is associated with the appearance in the culture of a cytopathogenic agent whose nature and properties are in large part essentially unknown. Whether this material, given the epithet of NACM for Naegleria amoeba cytopathogenic materials, is secreted and released by the amoeba, or whether it is a consequence of amoebic death and lysis, remains to be determined, as does the actual extent of its pathogenicity for cell cultures and for animals. It is proposed to produced sufficient amounts of purified NACM to permit studies of its chemical and physical nature and its biological activity in vitro and in vivo. Pathogenesis of the infection in experimental animals (primarily mice) will be followed by such techniques as immunofluorescence and immunoperoxidase staining, as well as (where indicated) by electron microscopy.